Chemical mass closure and assessment of the origin of the submicron aerosol in the marine boundary layer and the free troposphere at Tenerife during ACE-2

The organic, inorganic, mineral content and mass concentration of the submi cron aerosol were measured in June-July 1997 on Tenerife in the marine boun dary layer (MBL) and the free troposphere (FT). Aerosol size distributions were measured simultaneously at the same sites. The submicron aerosol mass concentrations derived from the chemical composition and calculated from th e number size distributions agreed within the experimental uncertainties bo th in the MBL (+/-47%) and the FT (+/-75%). However, the analytical uncerta inties in the concentration of organic compounds (OC) for the average sampl e collected in the MBL (-97, +77%) and the FT (+/-74%) were high. The avera ge contribution of aerosol various components to the submicron aerosol mass were calculated for different air masses. The absolute uncertainties in th ese contributions were calculated by adding random uncertainties quadratica lly and possibly systematic errors in a conservative way. In the unperturbe d MEL, the aerosol average composition (+/- the absolute uncertainty in the contribution) was 37 (-3, +9)% for non-sea-salt SO42- + NH4+, 21 (-2, + 10 )% for sea-salt, and 20 (-7, +11)% OC (N = 19). In the unperturbed FT, OC a nd SO42- accounted for 43 (+/-20)% and 32 (-5, +3)% of the submicron aeroso l mass, respectively (N = 15). Considering these aerosol compositions, we s uggest that the source for the FT aerosol could be the transport of contine ntal aerosol through precipitating convective clouds. A simple budget calcu lation shows, that in background conditions, the MBL and FT aerosol composi tions are consistent with the hypothesis that the MBL aerosol is formed by the dilution of continental aerosol by FT air, modified by deposition and c ondensation of species of oceanic origin. Dramatic continental aerosol outb reaks were observed in both the MBL and the FT. The aerosol outbreaks in th e MBL were due to transport of polluted air masses from Europe. They were c haracterized mainly by increases in SO42- + NH4+, making up 75 (-5, + 19)% of the submicron aerosol mass. The aerosol outbreaks in the FT were due to advection of desert dust, probably mixed with pollution aerosol.